For weeks, South Korean officials delayed expected announcements it would join, but experts say they had no other choice after Monday's underground nuclear weapons test by the North.

VOA: standard.2009.05.26

He suggests a recommitment by the nuclear powers not to test their weapons--there have been no nuclear tests since 1996--in exchange for a commitment by all nations to stop enriching uranium.

NPR: Nuclear Weapons Gain Importance for Regional Powers

The US imposed economic and military sanctions on India (and Pakistan) when it carried out its nuclear test in May 1998, and has since pressed both countries to sign the Comprehensive Nuclear Test Ban Treaty - but to no avail.

BBC: The US and India: Moving closer

In the test at the Bushehr nuclear power plant, "dummy" fuel rods were used, so no nuclear reaction began.

CNN: U.S.: Iran has material for nuclear bomb but still 'not close'